The class of devices that is magnetoelectronic devices is a broad class that includes motors, disk drives, and certain semiconductor memory devices, such as magnetoresistive random access memories (MRAMs), and integrated circuits that include MRAM and logic functions other than MRAM, such as radio and processing circuits. Memory devices of all types are an extremely important component in electronic systems. The three most prevalent semiconductor memory technologies are SRAM (static random access memory), DRAM (dynamic random access memory), and FLASH (a form of non-volatile random access memory), which are essentially non-magnetoelectronic. Each of these memory devices uses an electronic charge to store information and each has its own advantages. SRAM has fast read and write speeds, but it is volatile and requires large cell area. DRAM has high density, but it is also volatile and requires a refresh of the storage capacitor every few milliseconds. This requirement increases the complexity of the control electronics.
FLASH is the major nonvolatile memory device in use today. FLASH uses charge trapped in a floating oxide layer to store information. Drawbacks to FLASH include high voltage requirements and slow program and erase times. Also, FLASH memory has a poor write endurance of 104–106 cycles before memory failure. In addition, to maintain reasonable data retention, the thickness of the gate oxide has to stay above the threshold that allows electron tunneling, thus restricting FLASH's scaling trends.
To overcome these shortcomings, new magnetic memory devices are being evaluated. One such device is the MRAM, which stores bits as magnetic states. MRAM has the potential to have speed performance similar to DRAM. To be commercially viable, however, MRAM must have comparable memory density to current memory technologies, be scalable for future generations, operate at low voltages, have low power consumption, and have competitive read/write speeds.
A significant amount of power is consumed during a write operation of an MRAM cell in an MRAM device having an array of cells. The write operation consists of passing currents through conductive lines external but in close proximity to the MRAM magnetic element. The magnetic fields generated by these currents are sufficient to switch the magnetic state of the free layer of the magnetic element. In addition, as the bit dimension shrinks, the switching field increases for a given shape and film thickness, requiring more current to switch. As will be discussed in more detail below, data is stored in the magnetization state of the free layer of the magnetic element. Therefore a significant challenge to commercializing MRAM devices is to construct MRAM cells that switch the magnetic state using the lowest possible magnetic field, resulting in the lowest possible write currents, while maintaining the integrity of the data within the entire array of elements
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.